using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using static System.Buffers.Binary.BinaryPrimitives;

namespace PKHeX.Core
{
    /// <summary>
    /// Generation 3 <see cref="SaveFile"/> object for Pokémon Colosseum saves.
    /// </summary>
    public sealed class SAV3Colosseum : SaveFile, IGCSaveFile
    {
        protected internal override string ShortSummary => $"{OT} ({Version}) - {PlayTimeString}";
        public override string Extension => this.GCExtension();
        public override PersonalTable Personal => PersonalTable.RS;
        public override IReadOnlyList<ushort> HeldItems => Legal.HeldItems_COLO;
        public SAV3GCMemoryCard? MemoryCard { get; init; }

        // 3 Save files are stored
        // 0x0000-0x6000 contains memory card data
        // 0x6000-0x60000 contains the 3 save slots
        // 0x5A000 / 3 = 0x1E000 per save slot
        // Checksum is SHA1 over 0-0x1DFD7, stored in the last 20 bytes of the save slot.
        // Another SHA1 hash is 0x1DFD8, for 20 bytes. Unknown purpose.
        // Checksum is used as the crypto key.

        private const int SLOT_SIZE = 0x1E000;
        private const int SLOT_START = 0x6000;
        private const int SLOT_COUNT = 3;

        private int SaveCount = -1;
        private int SaveIndex = -1;
        private readonly StrategyMemo StrategyMemo;
        public const int MaxShadowID = 0x80; // 128
        private int Memo;

        private readonly byte[] BAK;

        public SAV3Colosseum() : base(SaveUtil.SIZE_G3COLO)
        {
            BAK = Array.Empty<byte>();
            StrategyMemo = Initialize();
            ClearBoxes();
        }

        public SAV3Colosseum(byte[] data) : base(data)
        {
            BAK = data;
            InitializeData();
            StrategyMemo = Initialize();
        }

        private StrategyMemo Initialize()
        {
            // Trainer1 = 0x00078;
            Party = 0x000A8;

            Box = 0x00B90;
            DaycareOffset = 0x08170;
            Memo = 0x082B0;

            // Since PartyCount is not stored in the save file,
            // Count up how many party slots are active.
            for (int i = 0; i < 6; i++)
            {
                if (GetPartySlot(Data, GetPartyOffset(i)).Species != 0)
                    PartyCount++;
            }

            var memo = new StrategyMemo(Data, Memo, xd: false);
            return memo;
        }

        private void InitializeData()
        {
            // Scan all 3 save slots for the highest counter
            for (int i = 0; i < SLOT_COUNT; i++)
            {
                int slotOffset = SLOT_START + (i * SLOT_SIZE);
                int SaveCounter = ReadInt32BigEndian(Data.AsSpan(slotOffset + 4));
                if (SaveCounter <= SaveCount)
                    continue;

                SaveCount = SaveCounter;
                SaveIndex = i;
            }

            // Decrypt most recent save slot
            {
                int slotOffset = SLOT_START + (SaveIndex * SLOT_SIZE);
                ReadOnlySpan<byte> slot = Data.AsSpan(slotOffset, SLOT_SIZE);
                Span<byte> digest = stackalloc byte[20];
                slot[^20..].CopyTo(digest);

                // Decrypt Slot
                Data = DecryptColosseum(slot, digest);
            }
        }

        protected override byte[] GetFinalData()
        {
            var newFile = GetInnerData();

            // Return the gci if Memory Card is not being exported
            if (MemoryCard is null)
                return newFile;

            MemoryCard.WriteSaveGameData(newFile);
            return MemoryCard.Data;
        }

        private byte[] GetInnerData()
        {
            StrategyMemo.Write().CopyTo(Data, Memo);
            SetChecksums();

            // Get updated save slot data
            ReadOnlySpan<byte> slot = Data;
            Span<byte> digest = stackalloc byte[20];
            slot[^20..].CopyTo(digest);
            byte[] newSAV = EncryptColosseum(slot, digest);

            // Put save slot back in original save data
            byte[] newFile = MemoryCard != null ? MemoryCard.ReadSaveGameData() : (byte[])BAK.Clone();
            Array.Copy(newSAV, 0, newFile, SLOT_START + (SaveIndex * SLOT_SIZE), newSAV.Length);
            return newFile;
        }

        // Configuration
        protected override SaveFile CloneInternal()
        {
            var data = GetInnerData();
            return new SAV3Colosseum(data) { MemoryCard = MemoryCard };
        }

        protected override int SIZE_STORED => PokeCrypto.SIZE_3CSTORED;
        protected override int SIZE_PARTY => PokeCrypto.SIZE_3CSTORED; // unused
        public override PKM BlankPKM => new CK3();
        public override Type PKMType => typeof(CK3);

        public override int MaxMoveID => Legal.MaxMoveID_3;
        public override int MaxSpeciesID => Legal.MaxSpeciesID_3;
        public override int MaxAbilityID => Legal.MaxAbilityID_3;
        public override int MaxBallID => Legal.MaxBallID_3;
        public override int MaxItemID => Legal.MaxItemID_3_COLO;
        public override int MaxGameID => Legal.MaxGameID_3;

        public override int MaxEV => 255;
        public override int Generation => 3;
        protected override int GiftCountMax => 1;
        public override int OTLength => 10; // as evident by Mattle Ho-Oh
        public override int NickLength => 10;
        public override int MaxMoney => 9999999;

        public override int BoxCount => 3;
        public override bool IsPKMPresent(ReadOnlySpan<byte> data) => PKX.IsPKMPresentGC(data);

        private static byte[] EncryptColosseum(ReadOnlySpan<byte> input, Span<byte> digest)
        {
            if (input.Length != SLOT_SIZE)
                throw new ArgumentException(nameof(input));

            byte[] output = input.ToArray();

            // NOT key
            for (int i = 0; i < 20; i++)
                digest[i] = (byte)~digest[i];

            using var sha1 = SHA1.Create();
            for (int i = 0x18; i < 0x1DFD8; i += 20)
            {
                for (int j = 0; j < 20; j++)
                    output[i + j] ^= digest[j];
                byte[] key = sha1.ComputeHash(output, i, 20); // update digest
                key.AsSpan(0, 20).CopyTo(digest); // for use in next loop
            }
            return output;
        }

        private static byte[] DecryptColosseum(ReadOnlySpan<byte> input, Span<byte> digest)
        {
            if (input.Length != SLOT_SIZE)
                throw new ArgumentException(nameof(input));

            byte[] output = input.ToArray();

            // NOT key
            for (int i = 0; i < 20; i++)
                digest[i] = (byte)~digest[i];

            using var sha1 = SHA1.Create();
            for (int i = 0x18; i < 0x1DFD8; i += 20)
            {
                byte[] key = sha1.ComputeHash(output, i, 20); // update digest
                for (int j = 0; j < 20; j++)
                    output[i + j] ^= digest[j];
                key.AsSpan(0, 20).CopyTo(digest); // for use in next loop
            }
            return output;
        }

        protected override void SetChecksums()
        {
            // Clear Header Checksum
            var headerCHK = Data.AsSpan(12);
            WriteInt32BigEndian(headerCHK, 0);
            // Compute checksum of data
            using var sha1 = SHA1.Create();
            byte[] checksum = sha1.ComputeHash(Data, 0, 0x1DFD8);
            // Set Checksum to end
            var checkSpan = checksum.AsSpan();
            checkSpan.CopyTo(Data.AsSpan(Data.Length - checkSpan.Length));

            // Compute new header checksum
            var header = Data.AsSpan(0, 0x20);
            int newHC = 0;
            for (int i = 0; i < 0x18; i += 4)
                newHC -= ReadInt32BigEndian(header[i..]);
            newHC -= ReadInt32BigEndian(header[0x18..]) ^ ~ReadInt32BigEndian(checkSpan);
            newHC -= ReadInt32BigEndian(header[0x1C..]) ^ ~ReadInt32BigEndian(checkSpan[4..]);

            // Set Header Checksum
            WriteInt32BigEndian(headerCHK, newHC);
        }

        public override bool ChecksumsValid => !ChecksumInfo.Contains("Invalid");

        public override string ChecksumInfo
        {
            get
            {
                byte[] data = (byte[])Data.Clone();
                var hc = data.AsSpan(12);
                int oldHC = ReadInt32BigEndian(hc);
                // Clear Header Checksum
                WriteUInt32BigEndian(hc, 0);
                using var sha1 = SHA1.Create();
                byte[] checksum = sha1.ComputeHash(data, 0, 0x1DFD8);
                var checkSpan = checksum.AsSpan();

                // Compute new header checksum
                var header = data.AsSpan(0, 0x20);
                int newHC = 0;
                for (int i = 0; i < 0x18; i += 4)
                    newHC -= ReadInt32BigEndian(header[i..]);

                newHC -= ReadInt32BigEndian(header[0x18..]) ^ ~ReadInt32BigEndian(checkSpan);
                newHC -= ReadInt32BigEndian(header[0x1C..]) ^ ~ReadInt32BigEndian(checkSpan[4..]);

                var chk = data.AsSpan(data.Length - 20, 20);

                bool isHeaderValid = newHC == oldHC;
                bool isBodyValid = chk.SequenceEqual(checkSpan);
                static string valid(bool s) => s ? "Valid" : "Invalid";
                return $"Header Checksum {valid(isHeaderValid)}, Body Checksum {valid(isBodyValid)}.";
            }
        }

        // Trainer Info
        public override GameVersion Version { get => GameVersion.COLO; protected set { } }

        // Storage
        public override int GetPartyOffset(int slot)
        {
            return Party + (SIZE_STORED * slot);
        }

        public override int GetBoxOffset(int box)
        {
            return Box + (((30 * SIZE_STORED) + 0x14)*box) + 0x14;
        }

        public override string GetBoxName(int box)
        {
            return GetString(Box + (0x24A4 * box), 16);
        }

        public override void SetBoxName(int box, string value)
        {
            SetString(Data.AsSpan(Box + (0x24A4 * box), 16), value.AsSpan(), 8, StringConverterOption.ClearZero);
        }

        protected override PKM GetPKM(byte[] data)
        {
            if (data.Length != SIZE_STORED)
                Array.Resize(ref data, SIZE_STORED);
            return new CK3(data);
        }

        protected override byte[] DecryptPKM(byte[] data)
        {
            return data;
        }

        protected override void SetPKM(PKM pkm, bool isParty = false)
        {
            if (pkm is not CK3 pk)
                return;

            if (pk.CurrentRegion == 0)
                pk.CurrentRegion = 2; // NTSC-U
            if (pk.OriginalRegion == 0)
                pk.OriginalRegion = 2; // NTSC-U
        }

        protected override void SetDex(PKM pkm)
        {
            if (pkm.Species is 0 or > Legal.MaxSpeciesID_3)
                return;
            if (pkm.IsEgg)
                return;

            // Dex Related
            var entry = StrategyMemo.GetEntry(pkm.Species);
            if (entry.IsEmpty) // Populate
            {
                entry.Species = pkm.Species;
                entry.PID = pkm.PID;
                entry.TID = pkm.TID;
                entry.SID = pkm.SID;
            }
            if (entry.Matches(pkm.Species, pkm.PID, pkm.TID, pkm.SID))
            {
                entry.Seen = true;
                entry.Owned = true;
            }
            StrategyMemo.SetEntry(entry);
        }

        private TimeSpan PlayedSpan
        {
            get => TimeSpan.FromSeconds((double)(ReadUInt32BigEndian(Data.AsSpan(40)) - 0x47000000) / 128);
            set => WriteUInt32BigEndian(Data.AsSpan(40), (uint)(value.TotalSeconds * 128) + 0x47000000);
        }

        public override int PlayedHours
        {
            get => (ushort)PlayedSpan.Hours;
            set { var time = PlayedSpan; PlayedSpan = time - TimeSpan.FromHours(time.Hours) + TimeSpan.FromHours(value); }
        }

        public override int PlayedMinutes
        {
            get => (byte)PlayedSpan.Minutes;
            set { var time = PlayedSpan; PlayedSpan = time - TimeSpan.FromMinutes(time.Minutes) + TimeSpan.FromMinutes(value); }
        }

        public override int PlayedSeconds
        {
            get => (byte)PlayedSpan.Seconds;
            set { var time = PlayedSpan; PlayedSpan = time - TimeSpan.FromSeconds(time.Seconds) + TimeSpan.FromSeconds(value); }
        }

        // Trainer Info (offset 0x78, length 0xB18, end @ 0xB90)
        public override string OT { get => GetString(0x78, 20); set { SetString(Data.AsSpan(0x78, 20), value.AsSpan(), 10, StringConverterOption.ClearZero); OT2 = value; } }
        public string OT2 { get => GetString(0x8C, 20); set => SetString(Data.AsSpan(0x8C, 20), value.AsSpan(), 10, StringConverterOption.ClearZero); }
        public override int SID { get => ReadUInt16BigEndian(Data.AsSpan(0xA4)); set => WriteUInt16BigEndian(Data.AsSpan(0xA4), (ushort)value); }
        public override int TID { get => ReadUInt16BigEndian(Data.AsSpan(0xA6)); set => WriteUInt16BigEndian(Data.AsSpan(0xA6), (ushort)value); }

        public override int Gender { get => Data[0xAF8]; set => Data[0xAF8] = (byte)value; }
        public override uint Money { get => ReadUInt32BigEndian(Data.AsSpan(0xAFC)); set => WriteUInt32BigEndian(Data.AsSpan(0xAFC), value); }
        public uint Coupons { get => ReadUInt32BigEndian(Data.AsSpan(0xB00)); set => WriteUInt32BigEndian(Data.AsSpan(0xB00), value); }
        public string RUI_Name { get => GetString(0xB3A, 20); set => SetString(Data.AsSpan(0xB3A, 20), value.AsSpan(), 10, StringConverterOption.ClearZero); }

        public override IReadOnlyList<InventoryPouch> Inventory
        {
            get
            {
                InventoryPouch[] pouch =
                {
                    new InventoryPouch3GC(InventoryType.Items, Legal.Pouch_Items_COLO, 99, 0x007F8, 20), // 20 COLO, 30 XD
                    new InventoryPouch3GC(InventoryType.KeyItems, Legal.Pouch_Key_COLO, 1, 0x00848, 43),
                    new InventoryPouch3GC(InventoryType.Balls, Legal.Pouch_Ball_RS, 99, 0x008F4, 16),
                    new InventoryPouch3GC(InventoryType.TMHMs, Legal.Pouch_TM_RS, 99, 0x00934, 64), // no HMs
                    new InventoryPouch3GC(InventoryType.Berries, Legal.Pouch_Berries_RS, 999, 0x00A34, 46),
                    new InventoryPouch3GC(InventoryType.Medicine, Legal.Pouch_Cologne_COLO, 99, 0x00AEC, 3), // Cologne
                };
                return pouch.LoadAll(Data);
            }
            set => value.SaveAll(Data);
        }

        // Daycare Structure:
        // 0x00 -- Occupied
        // 0x01 -- Deposited Level
        // 0x02-0x03 -- unused?
        // 0x04-0x07 -- Initial EXP
        public override int GetDaycareSlotOffset(int loc, int slot) { return DaycareOffset + 8; }
        public override uint? GetDaycareEXP(int loc, int slot) { return null; }
        public override bool? IsDaycareOccupied(int loc, int slot) { return null; }
        public override void SetDaycareEXP(int loc, int slot, uint EXP) { }
        public override void SetDaycareOccupied(int loc, int slot, bool occupied) { }

        public override string GetString(ReadOnlySpan<byte> data) => StringConverter3GC.GetString(data);

        public override int SetString(Span<byte> destBuffer, ReadOnlySpan<char> value, int maxLength, StringConverterOption option)
        {
            return StringConverter3GC.SetString(destBuffer, value, maxLength, option);
        }
    }
}